This unusual bulb is what I'll call a "transitional" bulb. The shape of this bulb is designed for an un
coiled tungsten cage filament. It is not the most efficient shape to use with a coiled filament. As you can see, there is a lot of wasted, empty space on the top portion of the bulb. But there's a coiled filament installed inside. The manufacturer used the old bulb shape, instead of the new shape meant for coiled filaments, which is the same shape that is still used today with traditional incandescent bulbs.
These "transitional" bulbs aren't likely to be worth a lot of money to a collector even when they are extremely rare. But I think it's still an odd & interesting item to have.
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